Belt tensioners of the type herein contemplated are exemplary of those used to tension the serpentine belt drive of a motor vehicle engine. Other types of tensioners contemplated are those used for timing belts. A tensioner of the type herein contemplated includes a fixed structure, which is usually fixed to the engine housing and a pivoting structure mounted on the fixed structure for pivotal movement about a pivotal axis. A spring is operatively connected between the fixed structure and the pivotal structure so as to pivot the pivotal structure in one direction about the pivotal structure. The pivoting structure carries a belt-engaging pulley for rotational movement about a rotational axis parallel with the pivotal axis. The pivotal movement of the pivoting structure applies a constant tension to the belt and to compensate for increases and decreases in the belt path length due to temperature changes and wear.
The fixed structure comprises a hollow shaft and an end member. The hollow shaft transmits the torque created by the spring to the end member. The end member comprises tensioner stops or locating pins that allow for the transmission of torque to the mounting structure. A common form of locating pins is a pair of diametrically opposed knobs protruding from the outward-facing surface of the end member. Since the entire magnitude of torque produced by the spring must be transmitted to the mounting structure through the joint between the end member and hollow shaft, a rigid joint is required between these members that is capable of resisting torque.
A common method currently employed for the purpose of joining the shaft and the end member is casting a positive torque retention feature into the end of a cast aluminum shaft. This allows the two elements to be joined, with material of the end portion of the shaft deformed over the outer surface of the end member. This practice creates a rigid joint capable of torque retention, but is limited to a cast aluminum shaft design. Additional operations may be added to create a torque retention feature on a steel shaft; however production costs are increased.
There is a need for a cost-effective method of producing a joint that is capable of high torque retention between a shaft and an end member of a tensioner and for a more cost-effective tensioner embodying such a joint.